The invention relates to a piston for a fluid operated setting device, in particular a linear drive or a shock absorber, comprising a support body, which possesses an annular recess whose axis coincides with the longitudinal axis of the piston, in which recess at least one annular permanent magnet arrangement is disposed. Furthermore the invention relates to a fluid operated setting device fitted with such a permanent magnet arrangement.
Subject matter of the type initially mentioned type is described for example in the German patent publication DE 3404095 C2. In this case it is a question of a linear drive in the form of a power cylinder driven by fluid power comprising a piston, secured to a piston rod, for transmission of the drive force. For detecting the position of the piston without contacting it physically the piston bears a permanent magnet arrangement in the form of an annular permanent magnet, which can cooperate with position detecting means carried on the housing. The permanent magnet is seated in an annular recess defined at the joint face between two axially connected piston parts. The assembly of the piston takes place on fitting to the piston rod, the annular permanent magnet also being placed between the two piston parts. In the case of such a design there is particularly the difficulty, in view of the complexity, due to the necessary integration of the permanent magnet arrangement and, of the piston structure and the involved assembly in connection with it.
The European patent publication EP 1058037 has therefore already made a proposal to produce the annular permanent magnet of plastic material filled with permanently magnetic components by injection molding including injection molding directly into an annular groove, accessible from the outside, in the support body of the piston. This is however dependent on a technically highly complex operation, which is only realistic with a substantial production volume.
The German patent publication 1 185 276 discloses a specially customized structure of a stator of an electric motor. This stator comprises a plurality of magnet segments, which are partially elastic and inserted axially into a cylindrical iron casing.